There are image forming apparatuses such as a multi-function peripheral (hereinafter referred to as “MFP”) and a printer. An image forming apparatus of one type includes a developing device which accommodates a developer. The developing device includes a developing roller. When air enters the inside of the developing device with the rotation of the developing roller, the pressure in the developing device may increase. When the pressure in the developing device increases, air containing toner in the developing device may spout out from the developing device. When air containing toner spouts out from the developing device, the toner may scatter outside the developing device, and a functional component such as a charger may be contaminated.